Engine retarding devices of the compression release type may utilized in work machines such as on-highway trucks and the like. A compression release brake assembly utilizes compression within the truck's engine to assist the truck's main braking system in order to slow the truck. In effect, such compression release brake assemblies convert the truck's internal combustion engine into an air compressor in order to develop retarding horsepower which is utilized to assist in slowing the truck.
Compression release brake assemblies which have previously been designed typically include a fluid system having a master cylinder having a piston which is actuated by a cam lobe or push rod associated with an exhaust valve, intake valve, or fuel injector corresponding to a first engine cylinder. Actuation of the piston associated with the master cylinder controls actuation of a piston associated with a slave cylinder which selectively opens and closes the exhaust vale of a second, different engine cylinder near the end of the compression stroke thereby causing the mechanical work performed during the compression stroke to be dissipated and hence not "recovered" during the subsequent power stroke.
In one embodiment of a hydraulically actuated compression brake, controlling the pressure of the hydraulic fluid may be useful in achieving the desired timing of the opening of the exhaust valve, with the desired force. As the cylinder pressure varies within a cylinder, the desired force for opening the exhaust valve also varies. Excessive exhaust actuation speed, which may be caused by excessive actuating fluid pressure, may cause a reduction in the service life of the exhaust valve. For example, if the actuating fluid pressure is too high, the lift of the exhaust valve may potentially overshoot and interfere with the piston, thereby potentially damaging the piston or valve. In addition, the faster the exhaust valve closes, which may be influenced by fluid pressure, the greater the velocity at which the exhaust valve seats. If the exhaust valve closes too rapidly, damage to the exhaust valve and/or the associated valve seat may occur. An inadequate actuating fluid pressure may result in the exhaust valve not being opened.
The present invention is directed to overcoming one or more of the problems identified above.